Refrigeration system defrosting by controlled flow of gaseous refrigerant



July 23, 1963 R. M. SHRADER 3,098,363

REFRIGERATION SYSTEM DEFROSTING BY CONTROLLED mow OF GASEOUS REFRIGERANT Filed Feb. 24, 1961 POWER LINES Exchanger HE C E VER COMPRESSOR INVENTOR WW Mw ATTORNEYS Kafmazzdll. JZI'MA United States Patent Office 3,098,363 Patented July 23, 1963 3,098,363 REFRKGERATION SYSTEM DEFROSTING BY CON- TRQLLED FLGW F GASEOUS REFRIGERANT Raymond M. Shrader, Decatur, Ga., assignor to Larki-n Coils, inc, Atlanta, Ga, a corporation of Georgia Filed Feb. 24, 1961, Ser. No. 91,528 6 Claims. (Cl. 62-151) The present invention relates to mechanical refrigeration systems of the type is which defrosting of the evaporator is accomplished by the periodic replacement of total refrigerant in the evaporator by hot refrigerant gas from the compression side of the compressor. This hot refrigerant is generally supplied to the evaporator by way of a branch conduit which taps the line from the high pressure side of the compressor to the condenser.

There are several drawbacks to this method of defrosting. The hot refrigerant gas, upon contacting the cold surface of the evaporator coil, may condense. As the condensate builds up in the form of liquid refrigerant, it may carry over into the suction line and thence into the compressor. As the liquid is incompressible, breakage of the compressor parts may result. This hazard is particularly great in systems in which the evaporator operates at temperatures below freezing, becoming greater as the temperature of the refrigerated space decreases. To provide for a sufiicient amount of refrigerant gas in the compressor-evaporator defrosting circuit, the condenser and receiver section of the refrigerating equipment must be open to the evaporator at the start of the defrost cycle. The pressure in the condenser and receiver is considerably greater than the pressure in the evaporator section of the system. This results in a flow, from the condenser section into the evaporator, of refrigerant which, because it is more highly saturated, is at a greater density than the refrigerant in the evaporator and suction side of the system. The influx of more highly saturated gas into the system, couplied with the fixed cubic volume pumping rate of the compressor, results in a relatively high weight per unit time pumping rate. As the defrost cycle continues, pressure equilibrium is rapidly reached as the compressor discharge pressure and the pressure in the condenser and receiver section equalize. When the branch conduit supplying hot gaseous refrigerant to the evaporator during the defrost cycle connects with the line from the high pressure side of the compressor to the condenser by a T or valve in an arrangement of conduits similar to that illustrated in the accompanying drawing, the more highly saturated or heavier gas particles tend to follow a straight path through the connection into the condenser while the lighter, less saturated gas particles more readily change course and flow through the branch conduit. Consequently, the density or weight per unit volume of the hot refrigerant gas circulating in the compressor-evaporator defrosting circuit gradually decreases. This gas, when pumped at a constant volume per unit of time, then exhibits a decreasing weight per unit time pumping rate. A fixed restriction in the form of a non-regulating valve or restricting device located in the defrosting circuit, therefore, cannot maintain a constant evaporator and compressor suction pressure in the face of the varying weight .per unit time gas flow, as the pressure differential across such a device is a function of the weight-flow through it.

A second point which must be considered in the prevention of liquid carry over into the compressor is that an accumulation of liquid refrigerant and oil or a combination of both may be lying in the evaporator coil at the start of the defrost cycle. A sudden, high velocity in-rush of hot refrigerant gas would cause the pick-up of this liquid and oil in the form of a slug which would then be carried over into the compressor.

Another difiiculty has been brought about by the recent introduction of several grades of compressors intended for use in various applications. Each grade of compressor is designed to pump a specific flow of refrigerant at specific pressure differential. That is, each grade of compressor is designed with a certain maximum suction pressure. Any deviation above this suction pressure will create an over-loaded condition leading to compressor stoppage. This condition is in no way related to the hazard of liquid carry-over into the compressor.

An object of the present invention, therefore, is the provision of a novel refrigeration system having hot gas defrosting means, wherein means are provided to maintain .a pressure within the evaporator which has a corresponding condensing temperature below the temperature of the refrigerant gas leaving the coils, thereby preventing the condensation of any amount of refrigerant in the evaporator.

Another object of the present invention is the provision of a novel refrigeration system having hot gas defrosting means, wherein means are provided to automatically and to constantly maintain the compressor suction pressure below the overload point for the various grades of machines upon which the evaporator coil and defrosting equipment may be operated.

Another object of the present invention is the provision of a novel refrigeration system having hot gas defrosting means, wherein means are provided to permit only a gradual build-up of flow of hot refrigerant gas into the evaporator at the begining of the defrost cycle;

Another object of the present invention is the provision of a novel refrigeration system having hot gas defrosting means, wherein means are provided to achieve maximum defrosting efficiency by operating the defrosting system at the highest evaporator pressure commensurate with pressure safety during the changing weight-flow rate through the defrost cycle.

The provision for a valve so placed that it automatically regulates the evaporator pressure and compressor suction pressure to a predetermined point during defrosting, and which permits a gradual build up of pressure within the system at onset of defrosting will be carried forth in this invention. Other objects of the invention will appear as the following description of a preferred and practical embodiment thereof proceed.

In the drawing:

FIGURE 1 is a diagrammatic lay-out of a refrigeration system embodying the principle of the invention;

FIGURE 2 is a cross-section through the T-fitting 25.

Referring now in detail to the drawing, the rectangle 1, designated by the broken lines, represents the refrigerated chamber in which the temperature is maintained below 32 F. Within that chamber is the evaporator 2, below which is a pan 3 for catching the water resulting from the defrosting, said pan discharging through drain pipe 4 which extends to the point 5 outside the refrigerated chamber. Said pan is heated during defrosting by an electrical means to prevent the formation of ice within. A fan '7 driven by the motor 8, circulates air through the evaporator and throughout the refrigerated chamber. Outside of the refrigerated chamber is a compressor 9 connected to the upper part of the evaporator by the suction line 14} and to the condenser 11 by the hot compressed gasous refrigerant pipe 12. The condenser is connected at its lower end to the receiver 13, the receiver being connected by the liquid refrigerant pipe 14- thr-ongh a normally open solenoid valve 20 the expansion valve 15 to the lower part of the evaporator. The compressor is driven by the motor 16. In the system as illustrated, the liquid refrigerant line 14 passes in heat exchanging relationship to the suction pipe 10' in the heat exchanger device 17, where the liquid is cooled by the gas in the suction line, whereby its refrigerating efficiency is enhanced. For the purpose of defrosting, branch conduit 18 leads from the hot gaseous refrigerant pipe 12 at a point between the compressor and condenser, through a regulating valve 26 and thence through the solenoid valve 20 into the pipe 15 adjacent the evaporator, bypassing the expansion valve 15'. For convenience there is a cutoff valve 119 at the lower end of the branch conduit 18 which is normally left open. Since the pan 3 and discharge pipe 4 within the refrigerated chamber are constantly within a freezing atmosphere, they are heated to keep the defrost water liquid until it reaches the outside of the refrigerated chamber. For heating the discharge pipe 4, the branch conduit 18 is substantially in heat exchanging relationship to the discharge pipe throughout the part of its extent which is within the refrigerated chamber.

The expansion valve 15 operates in response to a thermostatic bulb 22 against the suction line adjacent to the outlet end of the evaporator.

Defrosting is automatically accomplished by means of defrost control 23, the operation of which is outlined in United States Patent No. 2,688,850 assigned to Larkin Coils, Inc., Atlanta, Georgia, and will not be discussed in greater detail than is necessary to outline the salient features of this invention.

At the beginning of the defrost cycle, solenoid valve 2% is closed, preventing the admission of liquid refrigerant to the evaporator, and solenoid valve is opened, admitting hot gas to the evaporator for defrosting. The regulating valve 26, which is essentially connected in the branch conduit 18, is preferably an outlet pressure sensitive modulating valve, of known construction, which is responsive to downstream pressure to regulate flow therethrough. The valve 26 is so set at the initial adjustment of the system as to automatically regulate the pressure within the evaporator and the suction pressure of the com pressor at a point below the overload pressure of the compressor. The condensing temperature corresponding to this pressure will, in all cases, be below the temperature of the refrigerant gas leaving the evaporator, thus preventing any condensation of hot refrigerant gas within the evaporator. In the T connection 25, an orifice is placed at the termination of branch line 18, as detailed in FIG- URE 2, so sized as to prevent damaging overloading of the compressor in the event of total failure of the regulating valve 26 in the open position.

It may therefore be seen that the physical relationship of any of the components within the system, one with the other, have no bearing upon the proper functioning of this invention, but that efficient defrosting of the evaporator with the protection for the compressor depends only upon operating conditions within the system itself.

While but one preferred embodiment of the present invention has been particularly shown and described, it is apparent that various modifications may be made therein within the spirit and scope of the invention, and it is desired, therefore, that only such limitations be placed on the invention as are imposed by the prior art and set forth in the appended claims.

What is claimed is:

1. In a refrigeration system, a compressor, condenser, receiver, evaporator, expansion valve, and the usual suction line from the evaporator to the low side of the compressor, the hot gas line from the high side of the compressor to the condenser, the liquid line from the receiver to the expansion valve, and the connection from the expansion valve to the evaporator, means for defrosting the evaporator comprising a branch conduit from said hot gas line to the connection between said expansion valve and evaporator, a defrosting valve in said branch conduit normally closed when said system is in its freezing cycle, means for opening said defrosting valve periodically to effect defrosting, and an automatic downstream pressure responsive modulating valve in said branch conduit constructed to respond to the weight per unit volume gas flow of the gaseous refrigerant into the evaporator during the defrost cycle and adjusted to automatically regulate evaporator pressure and compressor suction pressure to a predetermined point during defrosting and to permit only a gradual build up of How of hot refrigerant gas into the evaporator at the beginning of the defrost cycle.

2. In a refrigeration system, a compressor, condenser, receiver, evaporator, expansion valve, and the usual suction line from the evaporator to the low side of the compressor, the hot gas line from the high side of the compressor to the condenser, the liquid line from the receiver to the expansion valve, and the connection from the expansion valve to the evaporator, means for defrosting the evaporator comprising a branch conduit from said hot gas line to the connection between said expansion valve and evaporator, a defrosting valve in said branch conduit normally closed when said system is in its freezing cycle, means for opening said defrosting valve periodically to effect defrosting, and an automatic downstream pressure responsive modulating valve in said branch conduit constructed to respond to the weight per unit volume gas flow of the gaseous refrigerant into the evaporator during the defrost cycle and maintain a pressure within the evaporator which has a corresponding condensing temperature below the temperature of the refrigerant gas leaving the evaporator to prevent condensation of refrigerant in the evaporator.

3. In a refrigeration system, a compressor, condenser, receiver, evaporator, expansion valve, and the usual suction line from the evaporator to the low side of the cornpressor, the hot gas line from the high side of the compressor to the condenser, the liquid line from the receiver to the expansion valve, and the connection from the expansion valve to the evaporator, means for defrosting the evaporator comprising a branch conduit from said hot gas line to the connection between said expansion valve and evaporator, a defrosting valve in said branch conduit normally closed when said system is in its freezing cycle, means for opening said defrosting valve periodically to effect defrosting, and an automatic downstream pressure responsive modulating valve in said branch conduit constructed to respond to the weight per unit volume gas flow of the gaseous refrigerant into the evaporator during the defrost cycle and adjusted to automatically regulate evaporator pressure and compressor suction pressure to a predetermined point during defrosting and to permit only a gradual build up of flow of hot refrigerant gas into the evaporator at the beginning of the defrost cycle, and means providing an orifice of fixed size within said branch conduit between said evaporator and said defrosting valve permanently determining a constant maximum rate of flow through said branch conduit, so calibrated with respect to the capacity of the system with which it is employed as to limit the rate of flow of hot gaseous refrigerant to said evaporator to the extent that it cannot condense in sufficient quantity to slug over into said suction line.

4. In a refrigeration system, a compressor, condenser, receiver, evaporator, expansion valve, and the usual suction line from the evaporator to the low side of the compressor, the hot gas line from the high side of the compressor to the condenser, the liquid line from the receiver to the expansion valve, and the connection from the expansion valve to the evaporator, means for defrosting the evaporator comprising a branch conduit from said hot gas line to the connection between said expansion valve and evaporator, a defrosting valve in said branch conduit normally closed when said system is in its freezing cycle, means for opening said defrosting valve periodcially to effect defrosting, and an automatic downstream pressure responsive modulating valve in said branch conduit constructed to respond to the weight per unit volume gas flow of the gaseous refrigerant into the evaporator during the defrost cycle and maintain a pressure Within the evaporator which has a corresponding condensing temperature below the temperature of the refrigerant gas leaving the evaporator to prevent condensation of refrigerant in the evaporator, and means providing an orifice of fixed size Within said branch conduit between said evaporator and said defrosting valve permanently determining a constant maximum rate of flow through said branch conduit, so calibrated with respect to the capacity of the system with which it is employed as to limit the rate of flow of hot igaseous refrigerant to said evaporator to the extent that it cannot condense in sufiicient quantity to slug over into said suction line.

5. In a refrigeration system including an interconnected compressor, a condenser, an evaporator, and an expansion valve positioned in operative relationship to the evaporator inlet, conduit means connecting the condenser outlet to the expansion valve for supplying refrigerant to the evaporator during the freezing cycle of the system, a suction conduit from the evaporator outlet to the suction side of the compressor, a hot gas conduit connecting the compressor discharge with the condenser inlet, means for defrosting the evaporator comprising a branch conduit from said hot gas conduit to the evaporator inlet between the evaporator inlet and said expansion valve, a defrosting valve in said branch conduit normally closed to prevent flow of hot gaseous refrigerant through said branch conduit when the system is in its freezing cycle, means for opening said defrosting valve periodically to admit hot gaseous refrigerant through said branch conduit to said evaporator inlet to effect defrosting, and outlet pressure responsive modulating valve means in said branch conduit operatively subject to pressure in said branch conduit between said modulating valve and the evaporator inlet for responding to the weight per unit time gas flow through said modulating valve to automatically and constantly maintain a pressure within the evaporator which has a corresponding condensing temperature below the temperature of the refrigerant gas leaving the evaporator.

6. In a refrigeration system including an interconnected compressor, a condenser, an evaporator, and an expansion valve positioned in operative relationship to the evaporator inlet, conduit means connecting the condenser outlet to the expansion valve for supplying refrigerant to the evaporator during the freezing cycle of the system, a suction conduit from the evaporator outlet to the suction side of the compressor, a hot gas conduit connecting the compressor discharge with the condenser inlet, means for defrosting the evaporator comprising a branch conduit from said hot gas conduit to the evaporator inlet between the evaporator inlet and said expansion valve, a defrosting valve in said branch conduit normally closed to prevent floW of hot gaseous refrigerant through said branch conduit when the system is in its freezing cycle, means for opening said defrosting valve periodically to admit hot gaseous refrigerant through said branch conduit to said evaporator inlet to elfect defrosting and outlet pressure responsive modulating valve means in said branch conduit operatively subject to pressure in said branch conduit between said modulating valve and the evaporator inlet for responding to the weight per unit time gas flow through said modulating valve to automatically regulate evaporator pressure and compressor suction pressure at a selected level during defrosting and respond to volume density as Well as flow rate of gaseous refrigerant through the branch conduit into the evaporator to permit only a gradual build up of flow of refrigerant into the evaporator at the beginning of the defrosting cycle.

References Cited in the file of this patent UNITED STATES PATENTS 2,688,850 White Sept. 14, 1954 2,934,911 Micai May 3, 1960' 2,944,411 McGrath July 12, 1960 2,957,316 Buchanan Oct. 25, 1960 OTHER REFERENCES Anderson, S. A.: Automatic Refrigeration, MacLaren and Sons, Limited, for Danfoss, Nordberg, Denmark, 1959, pages 183-186 and 210-212, TP49'2-A56. 

1. IN A REFRIGERATION SYSTEM, A COMPRESSOR, CONDENSER, RECEIVER, EVAPORATOR, EXPANSION VALVE, AND THE USUAL SUCTION LINE FROM THE EVAPORATOR TO THE LOW SIDE OF THE COMPRESSOR, THE HOT GAS LINE FROM THE HIGH SIDE OF THE COMPRESSOR TO THE CONDENSER, THE LIQUID LINE FROM THE RECEIVER TO THE EXPANSION VALVE, AND THE CONNECTION FROM THE EXPANSION VALVE TO THE EVAPORATOR, MEANS FOR DEFROSTING THE EVAPORATOR COMPRISING A BRANCH CONDUIT FROM SAID HOT GAS LINE TO THE CONNECTION BETWEEN SAID EXPANSION VALVE AND EVAPORATOR, A DEFROSTING VALVE IN SAID BRANCH CONDUIT NORMALLY CLOSED WHEN SAID SYSTEM IS IN ITS FREEZING CYCLE, MEANS FOR OPENING SAID DEFROSTING VALVE PERIODICALLY TO EFFECT DEFROSTING, AND AN AUTOMATIC DOWNSTREAM PRESSURE RESPONSIVE MOUDLATING VALVE IN SAID BRANCH CONDUIT CONSTRUCTED TO RESPOND TO THE WEIGHT PER UNIT VOLUME GAS FLOW OF THE GASEOUS REFRIGERANT INTO THE EVAPORATOR DURING THE DEFROST CYCLE AND ADJUSTED TO AUTOMATICALLY REGULATE EVAPORATOR PRESSURE AND COMPRESSOR SUCTION PRESSURE TO A PREDETERMINED POINT DURING DEFROSTING AND TO PERMIT ONLY A GRADUAL BUILD UP OF FLOW OF HOT REFRIGERANT GAS INTO THE EVAPORATOR AT THE BEGINNING OF THE DEFROST CYCLE. 